1. Field of the Invention
This invention relates to a metal-composite corrugated hose used for conveying fluid such as fuel or a refrigerant, and a process for manufacturing the same. More particularly, it relates to a metal-composite corrugated hose which is very high in fluid impermeability and satisfactorily high in flexibility and strength, and has a corrugated portion in which a metal layer is effectively protected against fatigue failure, and a process for manufacturing the same.
2. Description of the Related Art
Various kinds of rubber hoses have usually been used as fuel hoses for motor vehicles or the like because of their high vibration-absorbability and easy assembling or flexibility. The fuel impermeability of hoses has recently been considered to be very important for the protection of the environment. Attention has, therefore, been drawn to new types of hoses including a hose formed from a resinous material which is a better fuel barrier than rubber, and a hose having a curved or corrugated portion improving its vibration-absorbability and flexibility.
It is, however, likely that the regulations prohibiting the leakage of fuel by permeation may become still stricter in the future. It will also be necessary to consider measures against carbon dioxide used as a refrigerant, or hydrogen used in a fuel cell, leaking easily by permeation. It will, therefore, be necessary to consider a metal-composite corrugated hose formed from a metal and a resin. A preferred hose has a wall formed of a barrier metal layer and a reinforcing resin layer, and having a corrugated portion.
Japanese Patent Application Laid-Open No. 275981/1995 discloses a process in which a resin-coated corrugated tube is manufactured by coating a straight metal pipe with a resin layer and corrugated by drawing or hydro-forming.
When a metal pipe coated with a resin layer is deformed for corrugation, however, it is difficult to carry out the plastic deformation of the resin layer satisfactorily before the metal pipe is deformed without breaking (for example, while it has an elongation not exceeding 20%). It is, therefore, necessary to form the metal layer with a larger thickness and the resin layer with a smaller thickness, so that the metal layer may maintain its corrugated shape by overcoming any stress produced in the resin layer. A metal layer having a larger thickness, however, results in a hose which is more expensive, greater in weight and lower in flexibility, while a resin layer having a smaller thickness results in a hose which is so low in mechanical strength as to collapse easily when it is assembled.
The Japanese application referred to above discloses (1) a hose having a metal layer thickness of 0.5 mm and a resin layer thickness of 0.5 mm, (2) a hose having a metal layer thickness of 0.2 mm and a resin layer thickness of 0.7 mm, and (3) a hose having a metal layer thickness of 0.7 mm and a resin layer thickness of 1 mm. The hoses (1) and (3) are, however, low in flexibility because of their large metal layer thickness, though they are good in fluid impermeability. A serious problem on a metal-composite corrugated hose is usually the fatigue failure of the metal layer in its corrugated portion as a result of its repeated vibration and deformation, and it is necessary to reinforce it effectively with a resin layer.
The inventors of this invention have, however, found that the resin layers in all of the hoses (1) to (3) are too small in thickness to reinforce the metal layers satisfactorily and protect them from fatigue failure.
It is an object of this invention to provide a metal-composite corrugated hose which is highly impermeable to carbon dioxide, hydrogen, or any other fluid tending to leak easily by permeation, as well as conforming to stricter regulations prohibiting the leakage of fuel.
It is another object of this invention to provide a metal-composite corrugated hose which is sufficiently flexible for easy assembling and effective absorption of vibration, and at the same time sufficiently strong not to collapse when it is assembled.
It is still another object of this invention to provide a metal-composite corrugated hose having a resin layer which can reinforce a metal layer effectively against fatigue failure.
It is a further object of this invention to provide a process which can manufacture a metal-composite corrugated hose not having any of the drawbacks as pointed out before in connection with the prior Japanese application.
The inventors have found that it is important to select a metal layer thickness A and a resin layer thickness B each falling within a specific range and having a specific ratio to the other to obtain an improved metal-composite corrugated hose. The inventors have also invented a novel process for manufacturing an improved metal-composite corrugated hose.
According to a first aspect of this invention, there is provided a metal-composite corrugated hose having a wall comprising a metal layer as its innermost layer and a resin layer surrounding it, wherein the wall is at least partly corrugated and has in its corrugated portion a metal layer thickness A of at least 20 xcexcm, but below 200 xcexcm and a resin layer thickness B of 80 to 5,000 xcexcm, each thickness of A and B having a ratio (A:B) of 1:4 to 1:50.
The metal layer having a thickness A of at least 20 xcexcm in its wall portion to be corrugated can be corrugated satisfactorily without having any defects such as pinholes, while ensuring the impermeability of the hose to fuel, carbon dioxide, hydrogen, etc. Its thickness A below 200 xcexcm ensures the flexibility of the hose to enable easy assembling and effective absorption of vibration. The resin layer has a thickness B of at least 80 xcexcm which is satisfactorily large to ensure that the hose be strong enough not to collapse when it is assembled. Its thickness B not exceeding 5,000 xcexcm is small enough not to add undesirably to the weight of the hose.
As the resin layer thickness B is at least four times larger than the metal layer thickness A, the metal layer is not too large in thickness as compared with the resin layer, nor is the resin layer too small in thickness. Therefore, the resin layer can reinforce the metal layer very effectively to protect it from any fatigue failure resulting from the repeated vibration and deformation of the corrugated portion of the hose. The thickness B which is not over 50 times as large as A is not so large as to add undesirably to the weight of the hose. As the metal and resin layers have a good proportion in thickness to each other, the metal layer can maintain its corrugated shape by overcoming any stress produced in the resin layer, even if the hose may be manufactured by a known process as described in the prior Japanese application cited before. It is, however, more preferable to employ a process according to a third or sixth aspect of this invention for manufacturing the hose.
According to a second aspect of this invention, the metal and resin layer thicknesses A and B have a ratio of 1:4.5 to 1:10. This is a range in which the resin layer can reinforce the metal layer still more effectively without adding undesirably to the weight of the hose.
According to a third aspect of this invention, there is provided a process for manufacturing a metal-composite corrugated hose comprising the steps of:
(1) molding a resin hose having an at least partly corrugated wall from a thermoplastic resin;
(2) applying an adhesive to the inner surface of the resin hose; and
(3) fitting the resin hose in a hydro-forming mold having a correspondingly corrugated surface, inserting a metal tube into the resin hose and applying a hydro-forming pressure to the metal tube,
thereby forming a metal-composite corrugated hose having an at least partly corrugated wall comprising a metal layer defining its innermost layer and a resin layer surrounding it.
The process can be carried out without having any limitation imposed by the resin or metal layer thickness as encountered by the known process. There is no longer any problem in the formation of a corrugated shape even with a relatively small metal layer thickness, or a relatively large resin layer thickness. As it is possible to form both a resin and a metal layer with a desirable thickness, it is possible to avoid any metal layer thickness that would be so large as to add to the cost and weight of the hose and lower its flexibility, and it is also possible to avoid any resin layer thickness that would be so small as to lower the mechanical strength of the hose. The process ensures a high production efficiency, since it is easy to form a corrugated resin hose of high dimensional accuracy and bond a metal layer to its inner surface.
According to a fourth aspect of this invention, the hose has in its corrugated wall portion a metal layer thickness A of at least 20 xcexcm, but below 200 xcexcm and a resin layer thickness B of 300 to 5,000 xcexcm. Although the resin layer thickness may generally be still smaller, and range from 80 to 5,000 xcexcm, it is advisable to take into account any possible damage that may occur to the resin layer if the metal tube is subjected to hydro-forming in a corrugated resin hose as according to the third aspect of this invention. Thus, the resin layer preferably has a thickness of 300 to 5,000 xcexcm.
According to a fifth aspect of this invention, an outer surface of the metal tube to be subjected to hydro-forming according to a third or fourth aspect is treated in advance for improved adhesion to the resin hose. Thus, the fifth aspect of this invention enables further improved adhesion between the resin and metal layers.
According to a sixth aspect of this invention, there is provided a process for manufacturing a metal-composite corrugated hose comprising the steps of:
(4) shaping a metal tube so that it may have an at least partly corrugated wall; and
(5) forming a layer of a thermoplastic resin by powder coating or thermal spraying on the outer surface of the metal tube,
thereby forming a metal-composite corrugated hose having an at least partly corrugated wall comprising a metal layer defining its innermost layer and a resin layer surrounding it.
The process can be carried out without having any limitation imposed by the resin or metal layer thickness as encountered by the known process. There is no longer any problem in the formation of a corrugated shape even with a relatively small metal layer thickness, or a relatively large resin layer thickness. As it is possible to form both a resin and a metal layer with a desirable thickness, it is possible to avoid any metal layer thickness that would be so large as to add to the cost and weight of the hose and lower its flexibility, and it is also possible to avoid any resin layer thickness that would be so small as to lower the mechanical strength of the hose. The process is suitable for forming a resin layer having a still smaller thickness still more accurately.
According to a seventh aspect of this invention, the hose of the sixth aspect has in its corrugated wall portion a metal layer thickness A of at least 20 xcexcm, but below 200 xcexcm and a resin layer thickness B of 80 to 1,500 xcexcm. Although the resin layer thickness may generally have to be still larger and range from 80 to 5,000 xcexcm, the process according to the seventh aspect of this invention does not impose any limitation on the resin layer thickness, but allows it to be smaller and range from 80 to 1,500 xcexcm to thereby enable a reduction in weight of the hose.
According to an eighth aspect of this invention, the resin layer to be formed on the outer surface of the metal tube according to the sixth or seventh aspect is treated in advance for improved adhesion to the resin layer. Thus, the eighth aspect of this invention enables further improved adhesion between the resin and metal layers.
The above and other features and advantages of this invention will become more apparent from the following description.